Several forms of metallurgical furnace having a refractory, an outer steel shell surrounding the refractory, a roof, and a hearth are known in the art. Furnaces known in the art may be rectangular or square in horizontal section (when viewed from above or below), or may be round in horizontal section. Furnaces known in the art generally have a metal structure supported by the hearth and protected by the refractory, in which metal, slag, and other materials are to be heated. Above the heated metal and slag is an area of space referred to as “freeboard”, which is surrounded horizontally by the refractory. An electrical metallurgical furnace uses electricity for heating and melting. More particularly, in the typical round electrical metallurgical furnace, three electrodes are used to produce electric arcs for heating the contents of the hearth. In the typical electrical furnace, the refractory is typically made of stacked bricks.
The brick refractory typically serves to provide thermal insulation between different elements inside the furnace, including molten metal and slag as well as heated gas in the inner furnace space, from the surrounding environment. In furnaces known in the art, the temperature of the molten material may range from 1400 to 2200 degrees Celsius. In use, the inner surface of the brick refractory may be coated with a solid layer of “frozen” slag or deposited fumes and dusts, also referred to as a “skull”, which layer may be heated to a temperature in excess of 1000 degrees Celsius. The thickness of this “skull” will vary depending on the furnace power level and arc length, which is a function of voltage.
In some furnaces known in the art, gaps between the bricks of the brick refractory and cracks within the bricks tend to form over time and use, especially over the course of repeated heating and cooling cycles due to thermal stresses. Further, the brick refractory may be corroded or degraded due to chemical, thermal, and mechanical stresses caused by the properties of the molten metal and slag contained therein, resulting in eventual breakdown of the refractory from within. Gaps and cracks in the refractory may result in escape of molten metal from the furnace, into the brickwork of the refractory. Wearing down and breaking of the bricks may ultimately result in failure of the refractory. The risk of leak through the skull and then through spaces in the refractory, and eventually out of the furnace, is increased by the gaps between the bricks of the refractory.
In some furnaces known in the art, the roof fails to provide adequate thermal insulation for the surrounding environment. The roof may further fail to provide a barrier to prevent the escape of toxic gases, including carbon monoxide, into the surrounding environment, creating a potentially hazardous environment for workers.
In some electric furnaces known in the art, the high temperature created by the electrodes may unduly heat the roof. Additionally, the high voltage running through the electrodes may cause risk of electrocution for workers working near the roof.
The present invention generally addresses certain drawbacks of metallurgical furnaces known in the art.